From proving the power of brevity to providing a secret place in an age of unprecedented public exposure, here are Fast Company‘s Top 10 Most Innovative Companies in Social Media.

For proving the power of brevity–this time with video. Video sharing and social media were two separate things before Vine showed up on Twitter. Forty million users later, Vine has become a culture in and of itself. Marketers are studying Vine for insights into what their consumers care about and how to reach them, and it is still growing in spite of Instagram big-footing its way into the marketplace. The six-second videos are often ingenious, beautiful, or both, and thanks to a new feature called “revining,” added last summer, it is giving rise to a new breed of viral celebrities. Read more >>

For catching the under-25ers falling out of love with Facebook. Texting and Facebooking is so passé–at least for WhatsApp’s audience. As more parents (and grandparents) text and post status updates, their broods are looking for something cooler, and WhatsApp has easily elbowed to the front of a line of alternative messaging services. With 430 million monthly active users–up from 400 million in December–the company sends 50 billion messages per day. It’s accomplished this scale by charging only a nominal fee (free for the first year, 99¢ per year after) and never supporting ads. Features have evolved over the app’s four-year existence to include group chatting, location sharing, and voice messaging, ensuring that as SMS continues to decline, WhatsApp will reign as king for quite a while in its category. Read more >>

For taking chillingly aggressive steps to defend its social media perch. At 400 million registered users, Tencent’s WeChat is the giant among Chinese social messaging platforms, and in the last year, it’s taken an almost admirable aggressive stance to fend off attacks from challengers. In an attempt to further develop its own product ecosystem (à la Amazon), the company partnered with device maker Xiaomi to launch a phone aimed specifically at WeChatters, and in a clear warning to international competitors, offered 10 terabytes of free cloud storage to new foreign users. These are moves that its rivals, such as the declining Sina Weibo, can only dream of keeping up with.

For cultivating controversy into a cultural phenomenon. Like Vine, Snapchat has developed its own culture: It has transcended teen sexting and is now a medium unto itself. What began as a way to transgress risk-free has become a valuable tool for people to manage the overabundance of media in their lives–namely by getting rid of it. By the end of 2013, the service was fielding 400 million uploads per day–more than Facebook–up from 200 million in June.

For taking giant (social media) leaps for mankind. Perhaps scandal-prone brands could learn something from NASA when it comes to social media. The agency, which describes its followers as “customers,” manages its 480 different social media accounts so that mission updates and developments are communicated directly to users–not through news media. NASA’s Google+ Hangouts from the International Space Station, stunning Vine clips of erupting solar flares, and clever tweets from the Mars Curiosity rover have resulted in a social media presence that is nimble, beloved, informative, and full of personality. It boasts nearly 6 million Twitter followers and 2.5 million Facebook fans, and in the five months since it joined Instagram (home to astronaut Mike Hopkins’s famous space selfie), it has racked up 600,000 followers. Consultants and interns, take note.

For changing the dating game with a simple swipe. Tinder tapped into a vein of discontent with traditional online dating and has single-handedly upended the concept of virtual courtship. Innovation No. 1? Building the app on top of users’ existing social media presence, which streamlines the sign-up process and adds a measure of credibility to a potential sweetheart’s identity. Innovation No. 2? Leveraging touch screens with its dead-simple “swipe left, swipe right” functionality for those without much time to waste on plenty of fish. The app was getting 400 million swipes per day as of late November, and despite competition from upstarts like copycat Hinge, its popularity is holding firm.

For playing upon the love of trivia to build communities–and one of the year’s hottest games. On QuizUp, players can challenge best friends or total strangers in niche interests–from ancient Greece to Breaking Bad to Beyoncé. The result? An addictive, real-time trivia game that also establishes microcommunities of users who can chat, compare rankings, or discuss ideas on the more than 300 quiz topics available on the app. Within three weeks of its November launch, QuizUp had attracted more than 3 million users, becoming the fastest-growing iPhone game ever. Determined not to lets its hit become a fad like other mobile games, Plain Vanilla raised $22 million just after Christmas, and by the end of the year, QuizUp had been downloaded 5 million times. Call it a nod to the power of community.

For building a sounding board for showy social media users. Unlike (many) other social media aggregation tools, RebelMouse funnels posts into a Pinterest-like interface that lets users show off–instead of sift through–the content in their feeds. The tool is also easily embedded, which means RebelMouse can function almost as a personal home page, letting megabrands like Burger King and Pepsi display thousands of tweets and photos from happy customers. (Funded in part by superinvestor Ken Lerer, it’s also powering his daughter Izzie’s animal-rights site, the Dodo.) As of August, more than 300,000 sites had been built using RebelMouse, and unique visitors were up 900% compared with a year ago.

For providing a secret place in an age of unprecedented public exposure. The two-year-old secret-sharing app doesn’t disclose user numbers, but its monthly page views more than doubled over the course of 2013, from 1.5 billion in May to 3 billion by year’s end. The service is based on simplicity and anonymity: Write a few lines, choose an accompanying photo, and release your secret into the world. Fellow users can “heart” the images, and a staff of guardian editors keeps the tone positive. Toward the end of last year, founder Michael Heyward hired virality whisperer Neetzan Zimmerman (formerly of Gawker) to expand Whisper’s reach outside the confines of the app, setting up 2014 growth to be just as big–if not bigger–than what we’ve already seen.

For finally finding its way. After years of stagnant revenue growth, the location-based social network is showing signs of life, raising $35 million in Series D funding and adding 10 million new users in the second half of the year. A December redesign of the iOS app boosted usage by 60%, and in an aggressive move, it no longer allows private check-ins, making the app much more appealing to advertisers–which Foursquare began accepting in October. CEO Dennis Crowley and company are also experimenting with passive check-ins, in hopes of removing what many view as the service’s pain point. And it unveiled smart notifications that can serve up friends’ venue suggestions based on a user’s location.